Long Term Evolution (LTE) is an improved universal mobile telecommunication system (UMTS) that provides higher data rate, lower latency and improved system capacity. In LTE systems, an evolved universal terrestrial radio access network includes a plurality of base stations, referred as evolved Node-Bs (eNBs), communicating with a plurality of mobile stations, referred as user equipment (UE). A UE may communicate with a base station or an eNB via the downlink and uplink. The downlink (DL) refers to the communication from the base station to the UE. The uplink (UL) refers to the communication from the UE to the base station. LTE is commonly marketed as 4G LTE, and the LTE standard is developed by 3GPP.
In cellular networks, the inter-cell interference is commonly seen at a UE when a “desired” data transmission (i.e., one from the “serving cell”) is interfered by an interfering data transmission from a neighboring cell to another UE that has the neighboring cell as its “serving cell”. When the network deployment is synchronized among all cells with sufficient accuracy (e.g., to a GPS signal), the mobile receiver may attempt to cancel the interference in order to achieve a better throughput on the desired data transmission.
Starting from Apr. 2013, 3GPP started a new study item (SI), “Network Assisted Interference Cancellation and Suppression” (NAICS), to investigate the benefit on system throughput by leveraging receiver's capability of interference cancellation (IC). There are many methods for interference cancellation at the receiver, but typically, they all exploit some known or estimated characteristics of the interference data transmission such as the corresponding interference channel, the modulation order of the interference symbols, the coding information to possibly reconstruct the interference signal, and so on. Compared with interference-suppression receivers, IC-receivers usually need more transmission parameters of interference.
Commonly investigated IC techniques in literature may include symbol-level based IC (SLIC) and codeword-level IC (CWIC). SLIC is an IC technique that detects interfering signal, which is supposed to be finite-constellation modulated, in a per-symbol basis. CWIC is a technique in which a receiver decodes and re-encodes an interference codeword to reconstruct the contribution of the interference signal on its received signal. Compared to SLIC, a receiver needs more information on interference to access CWIC, such as the modulation and coding scheme (MCS) index and the rule for scrambling the bit stream of interference. Obtaining the interference characteristics, such as the modulation order or encoding rules of the interfering signal, is important for all IC techniques. The characteristics could be either blindly detected by victim receiver or informed from network side.
The challenge of interference cancellation lies on the fact that data transmission can be very dynamic in a neighboring cell due to the scheduling behavior of a base station when serving multiple UEs at the same time. As a result, interference may or may not be present from time to time depending on the traffic loading; different UEs may be scheduled at different time; the frequency resources allocated to a UE in an OFDMA based system (e.g., LTE) change from time to time; the modulation order and/or coding rate change according to the dynamic channel condition; and so on.
There are study results that showed promising gain assuming known or reliable detection of some transmission parameters of the interfering data transmission. However, the so-called “blind-detection” receiver can be very complex and unreliable if it must detect or estimate all the characteristics of a possible interfering data transmission, especially when the resources allocated to a data transmission can be very dynamic in both the time and frequency dimension as in LTE. Given the significant throughput gain from interference cancellation, especially for OFDMA-based networks such as LTE, there is a need to enable robust cancellation of neighboring cell's data transmission.